The blast happened in Logar province, some 10 kilometers (six miles) north of the capital, Pul-e-Alam, said Din Mohammad Darwesh, a spokesman for the provincial governor.

Darwesh said it appeared insurgents, who he identified as three Afghans and six Pakistanis, set off the bomb too early.

"Unfortunately, the explosion completely destroyed a nearby civilian house in which two women and two children were killed," he said in a telephone interview. "Police and local residents retrieved the bodies."

Two days earlier, additional Afghan soldiers had deployed to the capital of Logar Province after receiving an intelligence report about a possible attack.

Meanwhile Sunday, a lone suicide bomber entered a police station in southern Kandahar province, though officers' fire forced him to detonate his explosive vest early, only wounding one civilian, said Zia Durrani, spokesman for Kandahar's police chief.

Also in Kandahar, 12 Taliban escaped from the 1,200-inmate Kandahar Prison after a prison employee falsely put their names on a list of detainees who were scheduled for release, Durrani said. The men walked out of the prison and the prison employee has disappeared, he said. Two of the 12 have been recaptured, he added.

Kandahar Prison has seen spectacular escapes in the past. In 2011, more than 450 prisoners, many of them Taliban fighters, tunneled their way out of the prison and fled in buses that had been dispatched to collect them.

Southern Afghanistan, and Kandahar in particular, has been the site of some of the heaviest fighting in the protracted Afghan conflict as Afghan and international combat troops have tried to root out a stubborn insurgency. But the Taliban have been tenacious and most Afghans say they still rule in much of the countryside.

In the east of the country, officials said they are working to release elders kidnapped by armed men.

A spokesman in Nangarhar province, Ahmad Zia Abdulzai, said Sunday that 30 elders from the districts of Ghoshta and Lalpur had been kidnapped three days prior in a remote part of the Nangarhar.

He said that around 15 people already have been freed and that the kidnappers have demanded that any elders' relatives working for the Afghan police quit their posts.

Abdulzai did not provide further details on where or how the kidnappings were carried out.

No one has claimed responsibility for the kidnappings. Several armed groups operate in the area where the elders were taken.